This application relates and claims priority for all purposes to pending U.S. application Ser. No. 60/435,093 filed Dec. 20, 2002.
The invention relates to a system for broadcasting a deceptive radiation signature from an emissions producing asset such as an aircraft, for protection of the asset from radiation seeking vehicles. More particularly it relates to a synchronized, multi-source radiation broadcast system for emitting radiation signature patterns deceptive of the host asset""s actual position and path, while masking the normally emitted radiation signature, thereby confounding launches and inducing erroneous lead angle and flight path corrections in radiation seeking intercept missiles or other threat vehicles that are launched against it.
The Nov. 29, 2002 attack on a chartered Israeli Aircraft using SA-7 Missiles, has brought to attention the potential danger of portable surface to air missiles to the world""s airliners. While the SA-7s did not hit the Israeli Chartered Aircraft, the Israeli Airline, EI Al is believed to have protected their aircraft with electronic countermeasure systems for precisely that reason. Normally the SA-7 has a 20 to 70% chance of destroying the target aircraft. Effective countermeasures specific to the SA-7 and similar threats are available, but at a price of about two million U.S. dollars per aircraft. Some private, corporate, and selected government transport aircraft are equipped with such systems.
It is estimated that there are approximately over 6,000 unfired SA-7 Missiles in the world today and many are on the black market today at $5,000 a piece. There are also approximately 100 unfired U.S.-made Stingers remaining from the Soviet-Afghan war, which are more accurate than the SA-7s.
The SA-7 and Stingers incorporate an infrared (IR) guidance system that xe2x80x9cseesxe2x80x9d or senses the IR radiation signature or pattern of the target aircraft. The hot burning jet or turbine engines are typically the major contributors of the radiation. Once a signature pattern is placed within its field of view and the guidance system is initiated, it locks onto the signature and transmits guidance instructions to the missile flight control system. Well developed algorithms in the guidance systems provide a continuously updated lead angle for the missile trajectory based on sensed changes in direction and speed of the changes in the relative position of the target aircraft, or more precisely, its radiation signature.
The SA-7 and Stinger missiles are shoulder launched and are effective up to an altitude of 15,000 feet. They can be fired from the ground, from rooftops, boats, and vehicles anywhere in the landing or takeoff pattern of an aircraft.
IR countermeasure systems for aircraft have been developed to thwart these types of seeker missiles. Generally, an IR countermeasure system works by first detecting a missile launch, then initiating a spurious IR signature substantially more intense that that produced by the aircraft""s engines, from a location displaced from the aircraft. The source of the spurious radiation is typically ejected or otherwise physically removed or displaced from the immediate vicinity of the host aircraft, as by firing flares or towing a decoy. Thus, the IR guided missile is attracted towards the source of the spurious signature, away from the target aircraft.
Flares used in such systems are typically as much as 20 or more times higher intensity than the emissions being masked. Some threat vehicles are programmed to detect and reject a signature experiencing a very large difference in intensity, and scan for a lower level signature in the vicinity.
One available countermeasure system is available from Northrop Aircraft""s Rolling Meadow""s Division. Northrop uses a missile launch detector, detecting the missile exhaust plume, and directional IR Sources or lasers. Such a counter measures system may range in price between approximately two million dollars and three million dollars. Rafael, an Israeli-owned company, is offering a similar priced system, which takes 3 months to install. Another system employs an onboard transmitter in conjunction with the threat detection and identification system to send a command signal directly to the incoming missile to redirect it. BAE Information and Electronic Warfare Division, formerly Sanders Associates, offers an xe2x80x9celectric brickxe2x80x9d and xe2x80x9chot brickxe2x80x9d type systems, which modulate an electrical or fuel heated IR source to spoil the aim of the IR Missile.
Other countermeasure systems of note include that described in U.S. Pat. No. 4,990,920, issued to Royden C. Sanders, Jr., filed in 1983 and issued in 1991. The ""920 patent disclosed a missile detection system and a RF transponder onboard an aircraft and a towed decoy to separate the transponder. The system has been used with a decoy towed 300 feet behind the aircraft. The system has induced missile misses of 150-feet behind the towed decoy, protecting both the host aircraft and the towed decoy.
With the possible exception of EI AI, none of the world""s commercial airlines are equipped with IR Countermeasures. 6,000 Airliners have been built since 1996 and it is estimated that, worldwide, there are more than 9,000 Airliners flying. Lower cost alternatives to existing countermeasure systems would make equipping these airliners more feasible and ultimately make commercial flying safer.
For a more comprehensive understanding of the art, readers may find useful Vol 7. Countermeasure Systems, of The Infrared and Electro-Optical Systems Handbook, co-published by Environmental Research Institute of Michigan and the SPIE Optical Engineering Press, copyright 1993, revised printing 1996.
What is needed, therefore, are techniques for providing effective, and relatively low cost countermeasures systems for commercial aircraft, and for other fixed or mobile assets that normally emit a radiation signature as a necessary byproduct of their primary function, for evading radiation seeking vehicles of all types, including missiles.
The invention encompasses both apparatus and methodology, and is susceptible to numerous variations and embodiments. Embodiments of the invention encompass a multiple beacon system of two or more broadcast beacons mounted on the aircraft or other asset for providing a selective or general broadcast of deceptive radiation signature patterns for the protection of the aircraft from missiles equipped with a radiation seeking guidance system. The system emissions may be omni-directional, directional, or bidirectional, and have directionally discrete phasing or common field of view phasing as between beacons. The broadcast emissions may be time or altitude sequenced, based on departure or arrival time or altitude, so as to provide automatic coverage at times and places of highest threat potential.
There may or may not be supplemental or augmenting, ground based or airborne, onboard or remote, missile detection capability used to control or enhance the configuration and operation of the basic beacon system. The effects of a missile detection may be implemented in a simple configuration switching mode or may be applied in a continuous, real time control fashion, or some combination thereof so as to maximize the effects of the deceptive broadcast in the direction of the incoming missile. The most common contemporary threat as discussed above is seen to be operating in the IR (Infrared) range but the invention extends from the full infrared to ultraviolet range inclusively, to address alternative and evolving threats.
In its simplest form, the invention comprises a pair of beacons displaced on an aircraft, preferably one on each wingtip, with synchronized, alternating patterns of emission, at appropriate cycle times, of high and low level intensities of radiation at the wavelength of interest in the normally emitted signature; high level intensity being greater than the normal signature intensity of the aircraft. Using this sweep-modulated broadcast technique, an exaggerated zigzag pattern of intercept is induced, whereby an incoming missile is attracted to the first or lead-off beacon, then swept to the other or trailing beacon by the shifting center of intensity so as to erroneously interpret a lateral motion or displacement of the aircraft that in turn induces an erroneous and excessive lead angle at each zig; then zagging back to the lead off beacon when the broadcast cycle starts anew. When the missile closes with the aircraft such that the first or lead off beacon falls out of the missile""s field of view, the missile continues on its last erroneous lead angle, by which time it is likely too late to make a useful correction and the intercept fails.
A greater degree of assurance, effectiveness and protection is provided by the sweep modulation technique of the invention, with its deceptive indication of motion in a selected direction, rather than a simple alternating wingtip, high/low switching of emission levels with a bidirectional result. To this end, the basic system of the invention requires at least two aircraft-mounted radiation sources or transmitting beacons, displaced on or near a host aircraft such as one on each wingtip, or otherwise displaced on the airframe so as to bracket the span of the airframe as seen from the angle or direction of the approaching missile.
The beacons are modulated in a closely synchronized manner to generate a false infrared signature pattern with an intensity that masks primary sources of similar emissions on the host aircraft. To the missile launcher, the oscillating beacon pattern is inconsistent with the expected pattern of a target aircraft; inhibiting in some circumstances the acquisition of a xe2x80x9clock onxe2x80x9d signal required for missile launch. To the radiation sensors of a guided missile once launched, the false pattern indicates a continuous diverging of missile and aircraft trajectories as a lateral displacement motion of the aircraft from its actual position within the missile""s field of view. This apparent change in position causes the missile to generate an erroneous lead angle and intercept course of sufficient magnitude to take it outside the span of the beacons in the direction of the sweep of the modulation, so as to miss the aircraft.
As will be readily apparent, if the aircraft is in fact turning opposite or away from the direction of the modulation sweep with respect to the missile""s field of view during the final closure of the missile to the aircraft, or if the direction of the modulation sweep can be set or controlled so as to be opposite the direction of turn, the probability of a miss and the miss distance are both increased.
Since the system can be operated in a simple broadcast mode, no missile detection capability is required, and any number of incoming missiles will be similarly affected by the broadcast of the false signature. As noted above, the system operation and effectiveness can be enhanced by adding missile detection capability and using alternative beacon configurations, all as is discussed and illustrated herein.
As described above, vulnerability to man-portable and shoulder fired radiation seeking missiles is highest during take-off and landing operations, from the surface up to 15000 feet altitude. Missile shooters prefer to get a head-on or tail view of the aircraft engines where the IR signatures are strongest and where acquisition and firing tones will be sounded as a lock-on signal before firing. The immediate vicinity of runways and airports is generally protected against unauthorized access, but the zone of vulnerability to a surface based missile launch from ahead or behind the aircraft extends some distance out beneath the take off and landing zones. In order to achieve the desired effect, the beacon set of the Applicant""s system must be displaced across the apparent width of the aircraft or asset, on or near the structure with respect to the protected field or direction of approach, so as to substantially bracket the aircraft between the first and last beacons. For the best fore and aft zones of protection, this makes a wingtip to wingtip installation the basic configuration of choice. Of course other configurations are within the scope of the invention, depending on factors such as the aircraft or asset size and configuration, the normally emitted radiation signature pattern and intensity of the aircraft or asset, the desired zones of protection, and the type and performance characteristics of the threat vehicle.
As is well understood in the art, jet engine IR signatures of the engine metal at the inlet or outlet fall generally in the 1.5 to 2.5 micron region, or Band #1, which is the reason that threat missile guidance systems operate in this region. However, the jet engine plume is of greatest intensity in the Band #4 region of 4 to 5 microns, and some guidance systems utilize a Band #4 or a dual band sensor system to provide greater reliability of the tracking system. The invention is therefore inclusive of multi-band IR beacons.
As will be further appreciated by those skilled in the field, significant high intensity radiation at other than IR wavelengths may be detectable on or being emitted from various possible sources on an aircraft. Recognizing that multi-band sensors are not uncommon and may be expanded or revised to target other peak intensity wavelengths of the aircraft""s total radiation signature, the invention contemplates the use of single, dual and multi-band beacon systems that emit deceptive patterns of radiation in any mix of wavelengths from ultraviolet through long wave infrared inclusively, at which guidance systems may be known or developed to detect and track. The bands or wavelengths may be switchable or selectable in some beacons and some system configurations, to address different threats at different times and places.
It is therefore a goal of the invention to provide an asset or aircraft radiation broadcast system for inhibiting the target acquisition or xe2x80x9clock onxe2x80x9d function of a seeker in preparation for firing, and hence reducing the likelihood of the launch of a radiation seeking missile. It is likewise a goal of the invention to provide an asset or aircraft system for diverting incoming radiation seeking missiles from hitting the host aircraft or asset, by emitting a deceptive radiation pattern that evinces a displacement of the asset from its true position or path with respect to the incoming seeker. It is another goal to provide an automated such system independent of any missile or threat vehicle detection capability. It is yet another goal to provide a system of modulated onboard radiation beacons, particularly infrared beacons, of a total intensity that will mask the similar wavelength emissions from the aircraft, sweep modulated in closely synchronized combination such as to deceive a radiation seeking missile into making erroneous flight corrections to its lead angle and flight path so as to miss the aircraft and fail its intercept mission.
It is still yet another goal to provide a configurable aircraft system of multiple beacons working in conjunction with a missile detection capability for providing enhanced emission patterns of a deceptive signature. It is likewise a goal to provide an air transport system using airports configured with local area missile detection systems and missile warning transmitters in conjunction with aircraft configured with missile warning receivers and systems for broadcasting deceptive signature patterns.
A fundamental principle of the invention is to have at least two beacons located on or near the host asset or aircraft so as to position the host substantially between the beacons with respect to the field of view of a missile launcher or incoming radiation seeking missile. Another principle is to ramp down the intensity of one beacon as the originating or first beacon, from a maximum value greater than the intensity of the normal emissions of the aircraft to a threshold value, and to concurrently ramp up the intensity of the terminal or last beacon of the set from the threshold value to maximum. The sum of the intensity of the two or more beacons of the set remains at or above a level required to mask the normal emission signature of the aircraft.
This closely synchronized sweep modulation of the beacon system portrays to the guidance system a repetitive, apparent continuous shifting of the total pattern or center of the radiation. The sweep or movement of the center of intensity from one end to the other end of the beacon set is erroneously interpreted by the missile guidance system as a displacement of the aircraft in the direction of the beacon of increasing intensity, the last or the terminating beacon. The modulation profile or change of intensity at the beacons may be linear or otherwise; the sweep cycle time being intentionally designed to be within the guidance system""s ability to register as requiring a compensating change of lead angle.
Yet another principle of the invention is the inclusion of a snapback time at the end of the modulation cycle for resetting all beacons in the set to their respective initial high and low power settings. A snapback or reset time is sufficiently short that it has no significance to the missile or guidance system response time.
When this pattern of sweep modulation and snap back is repeated in synchronous fashion by the beacon set, the deceptive signature indicating an apparent movement in the selected direction causes the missile to make an oscillating or zigzag-like approach. The missile makes a long xe2x80x9czigxe2x80x9d for the duration of the sweep cycle to follow the deceptive signature sweep, and builds in a correcting lead angle that would lead to a missed trajectory by the guidance system. At the point that the sweep cycle ends and the snapback occurs, if the first beacon remains within the field of view of the seeker, the seeker may xe2x80x9cseexe2x80x9d the first beacon restart and begins a reversing xe2x80x9czagxe2x80x9d; a correction back towards the first beacon within the limits of its response time. The attempted course reversal or xe2x80x9czagxe2x80x9d is of short duration, however, as the sweep modulation immediately induces another reversing xe2x80x9czigxe2x80x9d in to direction of the signature sweep, with its longer duration, again inducing an erroneous correcting lead angle in the direction of the signature sweep. Eventually, when the missile is close enough, the originating or ramp down beacon, or beacons, fall out of the field of view. Thereupon, the missile continues on its last erroneous lead angle, taking it outboard of the last or most outboard beacon and wingtip, resulting in a missed intercept.
Still another principle of the invention is the expansion of the beacon set to a sufficient number of beacons that the modulation sweep is reduced to a simple, sequential, on/off cycle of each beacon synchronized as a sweep of intense emission from one end of the beacon set to the other. Stationary assets such as a nuclear plant or oil drilling rig may be more amenable to this protective approach than aircraft, for example. Several factors including the structural configuration, environment and operating characteristics of both the host structure and the threat vehicle, will determine the optimal beacon set configuration.
Yet another fundamental principle of the invention lies in the two different types of beacons or principle modes of modulating the respective beacon intensities. A first mode or beacon type employs an emitter or radiation source operated at uniformly maximum radiation intensity and confined by a moving mechanical mask or modulating screen, shutter or shield. The modulating mechanism may be operated in a manner that generates a directionally dependent instantaneous phase value or relative value of intensity as between the minimum and maximum emission intensities. A rotating shield embodiment with a window of varying width is disclosed below, although other forms of modulating screens in relative motion with respect to the radiation source arc within the scope and intent of the invention. One or more secondary shields may be use to provide a limited or selected field of effective radiation. These field of view shields may be stationary or directionally variable depending on system configuration. Other mechanical modulating mechanisms may generate an omnidirectional change in intensity between maximum and minimum limits. For example, a tube-like shield may be extended lengthwise to enclose or expose the emitter or radiation source.
A second mode of modulation employs electronic or direct modulation of the intensity of the emitter or radiation source of each beacon, as for example by modulating the input power or fuel flow, so that the phase or point in the modulation cycle is omnidirectional or independent of the direction from which the beacon set is being viewed or approached. No relative motion of a modulation screen, mask or shield is needed, although the source may be otherwise shielded to provide a limited or selected field of effective radiation as in the first mode. A xe2x80x9cflash lamp typexe2x80x9d IR source embodiment with source intensity modulation is disclosed below, although other types of sources susceptible of direct source modulation as for example by modulating the power input or a gating voltage or current, are within the scope and intent of the invention.
As will be apparent to those skilled in the art, the alternative modes of beacon modulation have implications with respect to multiple beacon configurations and selective beacon combinations as might be desirable particularly when the system is to be operated with variable or selectable directional priorities, or with a missile detection input that provides automated directional priorities. The reconfigurable multiple beacon embodiments disclosed below are indicative and not limiting of the scope of the invention in this regard.
The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and not to limit the scope of the inventive subject matter.